1. Field of the Invention
The present invention relates to a motor vehicle climate control system; and, more specifically to an apparatus that reduces air rush noise transmitted into the vehicle cabin or passenger compartment during operation of the system.
2. Description of Related Art
A motor vehicle climate control system or heating, ventilation air-conditioning (HVAC) system typically utilizes a blower to move and control airflow through the system. Air rush noise occurring in the HVAC system, especially when the blower is operated at high speeds; i.e., producing maximum airflow, is a customer comfort concern. In most vehicles, the operating mode generating the highest noise level is the recirculation mode with a high blower setting. The recirculation mode of the HVAC system draws air from the interior of the vehicle cabin or passenger compartment.
To operate the HVAC system in the recirculation mode, a recirculation door closes the fresh air inlet and opens the recirculation inlet enabling the HVAC system to draw air from the vehicle interior. Drawing air from the interior of the cabin not only provides a direct path for the inlet related noise but also traps other blower noises within the vehicle interior. Current recirculation doors used in climate control systems are a solid barrier of very stiff plastic or ABS material having a very low noise transmission loss. As a result, when the system is operating in the recirculation mode, it is almost 2-4 decibels louder than when operating in the fresh air mode.
One reason for the increased noise level is that when the recirculation door covers the fresh air inlet it prevents air rush and blower generated noise from escaping through the fresh air inlet to the exterior of the vehicle. Accordingly, closing the fresh air inlet audibly increases the noise level a perceptible amount as compared to operating the HVAC system in a fresh air mode, that is, when the recirculation door closes the recirculation air inlet and the fresh air inlet is open providing a path for noise to escape to the exterior of the vehicle.
It would be desirable to provide a recirculation door that enables passage of at least a portion of the air rush and blower noise to the vehicle exterior when the climate control system is operating in the recirculation mode.